Measurement of carbon dioxide and hydrocarbon fluxes from a Sitka Spruce forest using micrometeorological techniques

Abstract

CO 2 and hydrocarbon fluxes from a sitka spruce forest were measured using a conditional sampling method. The method was used in two ways: (1) an automated system was used to monitor continuously the mixing ratio difference of total hydrocarbons and CO 2 in sampling lines for updraught and downdraught air and (2) conditionally sampled updraught and downdraught air was passed through adsorption tubes, which subsequently were analyzed in the laboratory, to determine the fluxes of nonmethane hydrocarbons (NMHCs). Aerodynamic gradient measurements of NMHC fluxes were made over the same period. Method (1) produced a high temporal resolution data set of approximately 4 days of near-continuous fluxes. Marked diurnal trends in CO 2 flux were evident. Peak daylight photosynthetic fluxes ranged from -30 to -90 mmol m -2 h -1. Smaller fluxes were noted during heavy rainfall and diminished photosynthetically active radiation. Nighttime respiration ranged from 0 to 10 mmol m -2 h -1. Total hydrocarbon fluxes were 3 orders of magnitude smaller. During hot, sunny conditions a total hydrocarbon flux of approximately 400 pmol m -2 h -I (CH 4 equivalents) was observed. Fluxes of specific NMHC compounds, from method (2), ranged between 90 and 563 pg m -2 hour -1. The annual carbon flux to Great Britain's conifer forests was estimated to be 1.3 Mt using a simple upscaling model based on the observations of CO 2 flux during the field experiment. Edinburgh, Scotland. 2Institute of Terrestrial Ecology, Penicuik, Midlothian, Scotland. 3Institute of Environmental and Biological Sciences, Lancaster Universit),, Lancaster, England. forests to calibrate CCMs and to estimate the size of the sink are of great importance. Jarvis [1994] described measurements from sitka spruce in NE Scotland but indicated that there were few comparable published measurements of CO 2 excha,e between the coniferous forests and the atmosphere. Biogenic hydrocm'bon emissions also play an important role in atmospheric chemic;try and hence ultimately in the global radiation balance. For example, nonmethane hydrocarbon (NMHC) species represent an important sink for the hydroxyl radical which in mrn controls the atmospheric half-life of radiatively important gases such as CH 4 and oxides of nitrogen [Dw•er e/ al., 19911. However, much uncertainty surrounds the magnitude and distribution of the sources of these emissions on the global scale [Guenther et al., 1995]. Changes in mmospheric temperatures and precipitation patterns may result in enhanced emission of biogenic hydrocarbons w•th potential for complex feedback effects. Predictive modeling of such effects and their influence on global climate requires detailed knowledge of the primary mechanisms which control fluxes. Most of the early work [e.g., Zimmerman. 1979' [Finer et al., 1983] employed branch enclosure techniques wl•ich were scaled to represent the entire canopy. These enclosure techniques are subject to problems associated with heterogeneous canopies and unavoidable microclimatic disturbance within the cha...

Prerequisites for application of hyperbolic relaxed eddy accumulation on managed grasslands and alternative net ecosystem exchange flux partitioning

“…2. This has already been observed in previous studies (Baker et al, 1992;Beverland et al, 1996;Moncrieff et al, 1998;Ruppert et al, 2012).…”

“…But variations in b can be generated by just a small skewness of the JFD of w and c (Katul et al, 1996;Fotiadi et al, 2005;Ruppert et al, 2006b), the application to different trace gases (Businger and Oncley, 1990;Baker et al, 1992;Oncley et al, 1993;Pattey et al, 1993) or the use in different ecosystem compartments (Gao, 1995). b may also vary significantly during individual 30 min integration intervals (Businger and Oncley, 1990;Baker et al, 1992;Oncley et al, 1993;Pattey et al, 1993;Beverland et al, 1996;Katul et al, 1996;Bowling et al, 1999a;Ammann and Meixner, 2002;Ruppert et al, 2006b). Variations from 0.54 to 0.60 were found for several experimental data.…”

The use of relaxed eddy accumulation to measure biosphere-atmosphere exchange of isoprene and other biological trace gases

“…The statistical nature of the coecient has been addressed by Baker et al (1992), Wyngaard and Moeng (1992), and Katul et al (1996), but we do not yet understand the physical principles that underly its form. Studies in the past have taken two courses ± those which regress w H H versus r w up À dn for a large number of¯ux samples, then use a constant b (Baker et al 1992;Beverland et al 1996a), and those that calculate b for each run explicitly, often using a variety of scalars (Guenther et al 1996;Oncley et al 1993;Pattey et al 1993). Katul et al 1996 investigated the error associated with using b calculated from various scalars to calculate the¯ux of other scalars.…”

Atmospheric Removal Processes

“…Bussinger and Oncley (1990) developed a modified version of the accumulation method that relaxed the need for proportional valves. This method (relaxed eddy accumulation) has been used to measure deposition and emission rates of a variety of compounds for which fast chemical sensors are not yet common, such as pesticides (Majewski et al 1993), isoprene (Guenther et al 1996), peroxides (Hall 1997), and monoterpenes (Beverland et al 1996). Relaxed eddy accumulation is a promising technique likely to be used extensively in coming years until fast chemical sensors are available.…”